(i) It was first described in 1866 by J Langdon Down, so it is called Down's syndrome.
(ii) About 1 in every 750 children exhibits Down's syndrome throughout the world. It is also seen in chimpanzees and other related primates.
(iii) In humans, it comes as a result of non-disjunction of chromosome 21 during egg formation. The cause of this primary non-disjunction is not known.
(iii) The defect is associated with a particular small portion of chromosome 21. When this particular chromosome segment is present due to translation in three copies, instead of two, Down's syndrome occur.

(a) Why should we Conserve biodiversity :
1. Narrow utilitarian arguments Human being draw.direct economic benefits from nature like food,firewood, fibre, construction materials, industrial products, medicines etc.
2. Broadly utilitarian arguments.
Biodiversity plays major role in maintaining and sustaining supplyofgoodsand services(i) Amazonforests provide 20% of oxygen present in atmosphere. (ii) Ecosystemprovidepollinatores.
3.Ethical reasons. Every organism have intrinsic value even if there is no economicvalue. Conservation of biodiversity.
(b) Importance of biodiversity hot-spots and sacred groves They provide protection of species richness and high degree of endemism in natural Habitat.  Hot Spots are regions of igh level of species in their natural habitat. Sacret groves are forest tracts set aside and all trees and wildlife within area are giventotal protection.

(a) A develops into the embryo.
B develops into the endosperm.
(b) 1. The endosperm development starts from the primary endosperm cell containing the primary endosperm nucleus.
2. In the most common type of endosperm development, the primary endosperm nucleus undergoes successive free nuclear divisions to give rise to a number of free nuclei; at this stage, it is called free nuclear endosperm.
3. Subsequently wall formation takes place from the periphery and proceeds towards the centre and the endosperm becomes cellular.
4. This type of endosperm development is seen in coconut; the water of the tender coconut represents the free nuclear endosperm with thousands of nuclei in it and the white kernel around it represents the cellular endosperm.
5. In albuminous seeds, some amount of endosperm persists in the mature seed, as the developing' embryo does not consume it fully, e.g. wheat/maize.
6. In exalbuminous seeds, the endosperm is completely consumed by the developing embryo before seed maturation, e.g. groundnut and pea.

(a) Dryopithecus and Ramapithecus:
Characteristics:
(i) They were hairy.
(ii) They walked like gorillas and chimpanzees.
(iii) Ramapithecus was more man-like while Dryopithecus was more ape-like.
(b) (i) East African grasslands.
(ii) Homo habilis, Homo erectus and Neanderthals had brain capacities of 650-800 cc, 900 cc and 1400 cc, respectively.
(iii) During the ice age between 75,000-10,000 years ago.

The mature/functional insulin consists of two polypeptide chains, coded by two genes.
The American Company, Eli Lilly, prepared the two genes or DNA sequences coding for the two polypeptide chains.
The genes were introduced into the plasmid of bacterium E.coli.
The bacterium produces the polypeptides which are secreted in the medium.
They are isolated from the medium and combined by creating disulphide bonds into functional insulin.
Since, genetically engineered insulin does not induce any immunological response, unlike insulin from other non-human sources, it is preferred.

(a) (i) The polarity of the cutting would not have been correct.
(ii) It can be due to absence of buds.
(iii) The cutting may have been selected from a very old branch.
(b) (i) The cutting must be selected from a branch that is neither very old nor very young.
(ii) There should be enough number of buds.
(iii) The polarity of the cutting should be considered.
(iv) The season of growing must be properly selected.
(c) Bougainvillea, china rose, cotton, etc.(any two)
(d) Shanu's concern for fellow citizen and use of his knowledge for the benefit of the society

The bases of DNA sense strands from the promoter to the terminator sites from transcription unit

Sex-Linkage Or Sex-Linked Inheritance is the transmission of characters and their determining genes which are borne on the sex chromosomes and therefore are inherited together from one generation to the next.
Y-chromosome of male does not carry any gene other than TDF (testis determining factor).
It is estimated that in Drosophila melanogaster the X-chromosome (called X-linked genes bears) 150 genes while in human being it is 102.Two important sex-linked human diseases are hemophilia and colour blindness.The genes present on Y-chromosomes are called holandric genes.
Sex-linked inheritance was discovered by Thomas H.Morgan and named it as Sex-Linkage.

Puberty. The period at which the generative organs become capable of exercising the function of reproduction is called puberty.It extends from 12 to 17 years of age in human beings.

Ornithophily. Pollination carried out by small birds is called ornithophily. e.g. Australian plants.
Chiropterophily. It is pollination by bats. e.g. Sausage tree.​​​​​​​
Marcophily.  Snails also bring pollination, it is termed malacophily.

The separated DNA fragments are stained with ethidium bromide.
Then by exposure to UV-radiation, the separated DNAs become visible as orange-coloured bands.
The separated bands of DNA are cut out from the agarose gel and DNA is extracted from these gel pieces by the process known as elution

Sutton and Boveri.

  p \(\rightarrow\) 3, Q\(\rightarrow\)1, R\(\rightarrow\)2

RNA interference is a gene-silencing process that blocks the expression of genes in the parasite when it enters the host's body. 

The part of life cycle of Plasmodium spent in human body includes following stages:
(i) Sporozoites enter the human body through the bite of infected female Anopheles mosquito (vector)
(ii) From the blood, they enter liver cells and multiply within the liver cells.
(iii) Infected liver cells burst and release the parasites again in the blood.
(iv) They attack RBCs repeatedly, multiply and cause their rupture.
(v) Ruptured RBCs release a toxin called haemozoin which is responsible for high recurring fever and resultant chill/shivering.
(vi) When a female Anopheles mosquito bites an infected person, these parasites enter the mosquito body and undergo further development

These animals have insulating coat of hair or blubber or feathers to check loss of body heat.These animals regulate their body temperature by physiological means and maintain more or less constant internal temperature.They are, thus, termed endotherms.

The phenomenon is point mutation that involves substitution of a single nitrogenous base in DNA.

(a) Lactobacillus  
(b) Trichoderma polysporum  
(c) Yeast    
(d) Penecillin

Eutrophication
Eutrophication is defined as the process of nutrient enrichment of water and consequent loss of species diversity in water bodies.
1. Increased nutrient content of the water body causes algal bloom, i.e. excess growth of algae, especially cyanobacteria.
2. It covers the water surface, secretes toxins and reduces the dissolved oxygen content of water.
3. These toxins inhibit the growth of other algae and plants and cause death of aquatic animals.
4. Oxygen deficiency may be a cause for death of animals.

Polymerase Chain Reaction:
Multiple copies of the desired gene or segment of DNA, can be synthesised in vitro using two sets of primers, the oligonucleotides that are complementary to the regions of DNA of the two strands and the enzyme DNA polymerase.
This enzyme extends the primers using the nucleotides provided in the reaction and the genomic DNA as the template.
For repeated amplification to be achieved, a thermostable DNA polymerase (Taq polymerase), extracted from the bacterium, Thermus aquaticus is employed; it remains active during the high temperature treatment used for denaturation and separation of the two strands.

Convergent evolution:
It is the evolutionary process in which anatomically different organs in different groups of organisms, evolve towards the same function.
Analogous organs are the result of convergent evolution, e.g. Sweet potato (root modification) and potato (stem modification) are analogous, as they both are tuberous with stored food materials.
Divergent evolution:
It is the evolutionary process in which the same structure develops in different directions in different groups of organisms as adaptations to different needs.
Homologous organs are the result of divergent evolution, e.g. human hands are homologous to the wings of a bird, as their basic structure (number and types of bones) is similar. 

Biotortification refers to breeding of crops to produce varieties with higher levels of nutrients like vitamins, minerals,proteins or healthier fats.
The objective is to improve:
(i) Protein content and quality
(ii) Oil content and quality
(iii) Vitamin content and
(iv) Micronutrient and mineral content.
 Many nutrient-enriched varieties have been produced as given below.

(i) A-Spermatids, undergo spermiogenesis
(ii) A-Spermatids, B-Spermatogonium.
Spermatogonium (B) are diploid and have 46 chromosomes in humans, while spermatids (A) are haploid and have 23 chromosomes in case of human male.
(iii) E-spermatozoa, are motile cells
(iv) F-Sertoli cell, it provides nutrition to the germ cells
(v) Seminiferous tubule.